#include <iostream>
#include <typeinfo>
#include <cassert>
#include <any>

class Any
{
private:
    class holder
    {
    public:
        virtual ~holder() {}
        virtual const std::type_info& type() = 0;
        virtual holder* clone() = 0;
    };

    template<class T>
    class placeholder : public holder
    {
    public:
        placeholder(const T& val) :_val(val){}
        virtual const std::type_info& type() { return typeid(_val); }
        virtual holder* clone() { return new placeholder(_val); }
        T _val;
    };

    holder* _content;
public:
    Any() :_content(nullptr){}
    Any(const Any& other) :_content(other._content ? other._content->clone() : nullptr) {}
    template<class T>
    Any(const T& val) :_content(new placeholder<T>(val)) {}
    ~Any() { delete _content; }

    template<class T>
    T* get() 
    {
        assert(typeid(T) == _content->type());
        return &((placeholder<T>*)_content)->_val;
    }

    Any& swap(Any& other)
    {
        std::swap(_content, other._content);
        return *this;
    }

    template<class T>
    Any& operator=(const T& val)
    {
        Any(val).swap(*this);
        return *this;
    }

    Any& operator=(const Any& other)
    {
        Any(other).swap(*this);
        return *this;
    }
};

class Test
{
public:
    Test() { std::cout << "构造" << std::endl; }
    Test(const Test&) { std::cout << "拷贝构造" << std::endl; }
    ~Test() { std::cout << "析构" << std::endl; }
};

int main()
{
    // Any a;
    // {
    //     Test t;
    //     a = t;
    // }

    // a = 10;
    // int* pa = a.get<int>();
    // std::cout << *pa << std::endl;
    // a = std::string("hello world");
    // std::string* ps = a.get<std::string>();
    // std::cout << *ps << std::endl;
    std::any a;
    a = 10;
    int* pa = std::any_cast<int>(&a);
    std::cout << *pa << std::endl;

    a = std::string("hello world");
    std::string* ps = std::any_cast<std::string>(&a);
    std::cout << *ps << std::endl;

    return 0;
}